The present invention relates generally to an imaging module and an imaging reader for, and a method of, expeditiously setting one or more imaging parameters, such as exposure and/or gain values, of at least one imager for imaging targets to be electro-optically read by image capture over a range of working distances.
Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read targets, such as one- and two-dimensional bar code symbol targets, and/or non-symbol targets, such as documents. A handheld imaging reader includes a housing having a handle held by an operator, and an imaging module, also known as a scan engine, supported by the housing and aimed by the operator at a target during reading. The imaging module includes an imaging assembly having a solid-state imager or imaging sensor with an imaging array of photocells or light sensors, which correspond to image elements or pixels in an imaging field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged, and for projecting the return light onto the array to initiate capture of an image of the target. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electronic signals corresponding to a one- or two-dimensional array of pixel data over the imaging field of view. In order to increase the amount of the return light captured by the array, for example, in dimly lit environments, the imaging module generally also includes an illuminating light assembly for illuminating the target with illumination light in an illumination pattern for reflection and scattering from the target.
In some applications, for example, in warehouses, it is sometimes necessary for the same reader to read not only far-out targets, e.g., on products located on high overhead shelves, which are located at a far-out range of working distances on the order of thirty to fifty feet away from the reader, but also close-in targets, e.g., on products located at floor level or close to the operator, which are located at a close-in range of working distances on the order of less than two feet away from the reader. The reader may illuminate the far-out targets by emitting an illumination light at an intense, bright level, and capturing the return light from the illuminated far-out targets by employing a far-out imager having a relatively narrow field of view, and may illuminate the close-in targets by emitting the illumination light at a less intense, dimmer level, and capturing the return light from the illuminated close-in targets by employing a close-in imager having a relatively wide field of view. This variable illumination light level enables each such target to be more reliably imaged and successfully read.
However, the use of more than one imager and the variable illumination level presents a challenge to reader performance. For optimum reader performance, each target must be read by the correct imager; the correct imager should be set with one or more optimum imaging parameters, such as exposure values and/or gain values; and the illumination light should be set at an optimum illumination light level or value. These values are different for each imager, and vary, among other things, as a function of the working distance and of the illumination light level. Increasing the exposure and/or the gain values of the imager, as well as increasing the illumination light level, will increase the captured image brightness of the image of the target, and vice versa.
In order to set an imager with one or more optimum imaging parameters, it is known for the imager to capture an entire image from the target, to analyze the brightness of the entire image, to change the imaging parameters based on the analysis of the entire image, to capture another entire image from the target, and to repeat all the steps of this process for as many times as it takes until the brightness of the entire image is within an acceptable level. An automatic exposure controller (AEC) is typically used to control the imager's exposure, and an automatic gain controller (AGC) is typically used to control the imager's gain. A typical known strategy is to use exposure priority, in which the exposure is increased first until a maximum exposure time or threshold (typically around 4-8 ms in order to reduce hand jitter motion effects for a handheld reader) is reached. If the image brightness is still too low, then the gain is increased. This strategy maximizes the signal-to-noise ratio (SNR) of the imager, because the gain is only increased when necessary. Although generally satisfactory for its intended purpose, this known process is very slow and inefficient in practice, especially when more than one imager is involved, and when the entire known process has to be repeated for each additional imager. Reader performance can be deemed sluggish, and is unacceptable in many applications.
Accordingly, there is a need to expeditiously select the correct imager in such readers, to expeditiously set the selected imager with one or more optimum imaging parameters, and to expeditiously set the illuminating light assembly to illuminate the target with illumination light at an optimum illumination light level, in order to more rapidly, efficiently, reliably, and successfully read both far-out targets and close-in targets with the same reader.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.